High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described inter alia in Whinfield et. al., U.S. Pat. No. 2,465,319 and in Pengilly U.S. Pat. No. 3,047,539. These patents disclose that the polyesters are particularly advantageous as film and fiber formers.
From U.S. Pat. Nos. 3,304,282; 3,396,142; 3,408,225; 3,437,632; 3,671,487 and 3,678,079, it is known to prepare glass fiber reinforced thermoplastics.
Also, it is known to add a foaming agent to thermoplastics as disclosed in U.S. Pat. Nos. 2,964,794; 3,268,636; 3,277,029; 3,290,261; 3,377,296; 3,436,446; 3,442,829 and British Pat. No. 838,824. Additionally, U.S. patent 3,334,154 discloses a polymer composition employing a flame-retardant additive comprising a copolymer. However, none of these references discloses a composition comprising a polyester, a filler selected from the group consisting of fibrous glass and a mineral or mixtures thereof, a flame-retardant additive and a minor amount of a foaming agent.
It has been discovered that the instant flame-retardant injection moldable composition comprising in admixture: (a) polyester resin, (b) a filler selected from the group consisting of fibrous glass or a mineral or mixtures thereof in an amount of from about 5 to about 50 weight percent; (c) a flame-retardant additive in minor proportion but in an amount at least sufficient to render the polyester resin non-burning or self-extinguishing and (d) a minor amount of a foaming agent, provides polyester products which have uniform cell structure, smooth surfaces, high impact, modulus and tensile strength. Also, the composition of this invention has an SE-O Rating in UL's Vertical Burning Test for Classifying Materials.
When foaming agent is added directly to a polyester, highly irregular foaming occurs which results in an inferior product. However, when the foaming agent is added to a polyester containing a filler such as fibrous glass or a mineral or mixtures thereof, and a flame retardant additive in an amount of at least 5 weight percent, a foamed product is produced having a rigid cellular core within a solid integral skin having the outstanding properties listed above.
The composition of the instant invention is injection molded in a standard injection molding machine to produce a variety of foam molded products.